Sean Sheppard

hi,
I've just bought a used Bravo One package to combine with my GM 350 engine.
Do i still need to use the Alpha shift interrupter switch on the Bravo Drive?

Jeff Pierpont

Sean , bravo units do not have interrupts only the alpha models, the wiring harness should have a purple wire jumper on the rear starboard side plug which is used for a bravo.Jeff

Mr Gadgets

Sean,
The Bravo is much beefier unit, and therefore doesnt need the interrupter switch. You can bypass it. That is not to say that you can put a Bravo in gear at over 1000rpm and not do damage. Let it idle down before you shift and you wont have any problems..

Hope this helps
Dick

Hang Time 27

More info:

Alpha unit used cutoff/interupt to take pressure off gears/"dog teeth" to allow you to shift in and out of gear. There is a physical interlocking of gear "teeth" whem shifting, and without the interupt, your stuck in or out of gear while engine is running.

Bravo unit has "cone clutch" setup instead. The units gears fit together like two drinking glasses, with the pressure causing the one "glass" to spin the other and your in gear, but....... if you push them together too hard by shifting at @1,000 rpm or higher, they can get stuck together, forever, and you would be stuck in that gear. But there is no teeth to mesh together when going into or out of gear, so no interupt is used.

Pismo10

I agree with hang time, it has nothing to do with the "beefiness" of the drive. They are two totally different designs, the Alpha needs the interrupt to work and the Bravo does not.
Unhook it.

Mr Gadgets

I stand corrected, thank you gentlemen! I have never disassembled an Alpha, but have had many Bravo's apart. I assumed the Alpha needed it because it is a weaker drive, shame on me. I know one needs it and the other doesn't, the why is the irrelevant part.. But you guys are correct. Did not mean to miss lead anyone.

Thanks
Dick

Hang Time 27

Don't worry you weren't misleading. and yes I agree that the alpha drive is an irrelevant part

mcollinstn

Take your hands and make "monster claws" with em. You know where your fingers are all sticking forward like a spider's legs. Pretend the fingers are metal. Face your two hands together. Pretend there is a shaft running thru them. Your left hand is the forward drive gear and is being spun by a pinion from above. The left gear/hand is on a set of bearings on the propshaft and spins freely on it. The right hand is splined to the propshaft. It slides back and forth left and right. If you slide it towards the left, you can see that the fingers/dogs will lock together, which transfers power from the gear.

Picture the left hand spinning. Move the right hand into it. Thunk. You just put an Alpha into gear. Now put pressure on the two hands and you'll see that it is "hard" to pull it back out of gear due to the friction between the fingers. That's why there is a shift interrupter. Kill the spark and the load is gone. Shifts right out freely.

The dog shoft lower unit has been around forever and is on most every outboard. Big hp 2 stroke V-6's get away with no interrupter because they idle unevenly. Rumpa rumpa rumpa. The lumpy idle gives an opportunity to unload the dogs and allow a shift to occur. V8 350 Chevys idle too smoothly to unload the dogs. So an interrupter was the obvious band aid.

I honestly don't know if the big smooth idling 4 stroke outboards use an interupter but I wouldn't be surprised if they did...

Hang Time 27

Also,
Interesting difference between the way Mercruiser and OMC handled the interupt on thier otherwise similar designs. Merc was actually shorting or killing the ignition momentarily, while the OMC's actually had a rev limiter/control box that acted just like a MSD rev control, cutting the rpms to 400 by cutting out every other cylinder. The OMC box works much better than the Merc setup if your putting in a bigger cam with some lope to it.

Of couse both Co's changed their design to the cone clutch the day Volvo's patent ran out......

Sean Sheppard

Thanks everyone,
You have all been very helpful, and yes I have lowered the idle speed to 700rpm, and she shifts ever so sweetly.
Sean